Simulative temperature controller for a motor vehicle

ABSTRACT

A heating device for use in motor vehicles to rapidly heat combustion chambers, exhaust gas sensors, catalyzers and other associated apparatus. A resistive heating element is connected in series with a low-impedance measuring resistor and a switch across a power source, while a resistance bridge is formed with the aid of two further resistors. The diagonal bridge voltages are compared in a comparator whose output actuates a control circuit which operates the heater switch. The heater switch also provides the power for the comparator. In a first interval, constant current is applied to the heating element, while the current is pulsed during a second time interval. The switch control pulses may be provided by a free-running oscillator or one whose pulses are synchronized with the undulations of the engine starter current.

This is a continuation of application Ser. No. 350,548 filed Feb. 19,1982, which is a continuation of Ser. No. 128,765 filed Mar. 10, 1980,now U.S. Pat. No. 4,348,583, which is a continuation of Ser. No.898,758, filed Apr. 20, 1978, now abandoned.

Cross-reference is made to the U.S. patent application, Ser. No.166,925, of Bube et al, filed Apr. 7, 1980, describing a safety devicefor an electric consumer in a motor vehicle which includes a temperaturesimulating circuit similar to the temperature simulating circuitdescribed herein.

BACKGROUND OF THE INVENTION

The invention relates to the field of motor vehicles. More particularly,the invention relates to apparatus for providing rapid heating ofportions of the engine or of its associated elements, such as theexhaust gas catalyzer. In a known electrical heater of this type, aheating element is connected in series with a bimetallic switch and aresistor. At the beginning of the heating cycle, the resistor isshort-circuited and is later introduced into the circuit when thebimetallic switch has responded to the ambient temperature. It is aparticular disadvantage of the known heating apparatus that high poweris required even in the secondary heating period. Furthermore, the knownapparatus provides no practical way to change the heating powergenerated during the second heating period.

OBJECT AND SUMMARY OF THE INVENTION

It is thus a principal object of the present invention to provide anelectrical heating apparatus for heating various elements of an engineor accessory equipment in a motor vehicle. It is a further principalobject of the invention to provide a heating apparatus in which thepower used by the heater is reduced during a second heating interval.Yet another object of the invention is that the average heating energyduring a second heating interval can be controlled with relative ease.Yet another object of the invention is a heating apparatus in which thetemperature of the heating element can be adapted to the requirements ofthe engine during starting and warm-up without regard to the voltagesupplied by the vehicle battery.

These and other objects are attained according to the present inventionby providing a heating apparatus in which a heating element receives apredetermined amount of power during a first timing interval andwherein, during a second and consecutive timing interval, the heatingcurrent is delivered to the heater as a series of pulses.

It is a further object of the invention to so deliver power to theheater during the second heating interval that the total currentsupplied by the battery is reduced and the load on the battery is thusreduced during that time. This object is attained by synchronizing thepower pulses delivered to the heater in the second heating interval withthe decreases of the starter current of the engine. The duration of thefirst heating interval may be determined in a variety of ways. Accordingto the present invention it has been shown to be particularlyadvantageous if the effective resistance of the heating element ismeasured, for example in a resistance bridge. However, the heatingprocess may also be electrically simulated.

The heating device according to the present invention may also be usedto serve as a glow heater in self-ignited engines, and it may find useas a heater for heating exhaust gas detectors which are known to requirea relatively elevated temperature for correct functioning.

The invention will be better understood as well as further objects andadvantages thereof become more apparent from the ensuing detaileddescription of a number of preferred embodiments taken in conjunctionwith the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a set of diagrams illustrating in FIG. 1a the temperature ofthe heating element as a function of time and in FIG. 1b the heatingcurrent as a function of time;

In FIG. 2a is shown a diagram illustrating the starter current as afunction of time, FIG. 2b shows the heater current as a function of timeand FIG. 2c is a diagram of the overall battery current as a function oftime;

FIG. 3 is a block diagram of a first exemplary embodiment of the heatingdevice of the present invention;

FIG. 4 is a block diagram of a second exemplary embodiment of theheating device according to the invention;

FIG. 5 illustrates five different variants for operating the heateraccording to the invention;

FIG. 6 is a detailed circuit diagram of the apparatus shown in FIG. 3;and

FIG. 7 is a detailed circuit diagram of the apparatus shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The diagrams shown in FIG. 1 serve to illustrate the basic principle ofthe present invention for operating a rapid heating device according tothe present invention. As illustrated in FIG. 1a, it is desired that thetemperature of the heating element rise rapidly after which it is heldat a predetermined level. The heating power required to obtain thistemperature behavior is illustrated in FIG. 1b. It will be seen that,during the initial heating phase, there is provided a constant heatingcurrent, while in the second heating phase, where the temperatureremains nearly constant, the heating current is delivered as a series ofpulses. There are thus two distinct time intervals during the heatingprocess.

It is easily understood that a rapidly acting heater requires arelatively high power. However, when such heaters are used in motorvehicles, care must be taken that the battery is not overloaded,especially during the engine starting process. It is thus desirable, asillustrated in FIG. 2, to synchronize the power pulses for the heaterwith the minima in the starter current of the engine. The cause of thecyclic variations in the starter current, as shown in FIG. 2a, is theperiodically varying resistance of the engine to the starting effort,due to the compression which occurs in the various cylinders. If theoccurrences of the heating current pulses are made to coincide with theminima in the starter current, as illustrated by the FIG. 2b, the totalbattery current will follow a curve illustrated in FIG. 2c. It will beappreciated that the overall current amplitude has been substantiallyleveled out.

The block diagram of FIG. 3 which illustrates a first embodiment of theinvention includes a heating element 10 and a switch 11. A measuringresistor 12 is connected between these two elements and the entireseries connection is placed between the positive and negative poles 14and 15, respectively, of a power source. Two bridge resistors 16 and 17are placed in parallel with the measuring resistor 12 and the heatingelement 10. The junction of the heating element 10 and the resistor 12is connected to one input of a comparator 18 while its other input isconnected to the junction of resistors 16 and 17. The output of thecomparator 18 is coupled to a switching circuit 20 which actuates theswitch 11. A pulse generator 22 is also coupled into the switchingcircuit 20. The generator 22 may be a freely oscillating pulse generatoror it may be synchronized by synchronizing pulses received from acomparator 24, as actuated by the starter 25.

The synchronization of the circuit may also take place on the basis ofmodulations in the supply current.

The rapid heating device illustrated in FIG. 3 operates as follows: Thepulse generator 22 causes the switching circuit 20 to close the contact11 for a short period of time, for example 10 ms. As a consequence, thebridge circuit consisting of resistors 16, 17, 12 and the heater element10, as well as the comparator 18, are supplied with power and the outputof the comparator 18 now holds the contact 11 closed until such time asthe increasing temperature of the heating element 10 has caused thebridge to be balanced. At that point, the circuit 20 causes the switch11 to be turned on and off at the frequency of the output signal fromthe generator 22. This output signal may be independent of the startercurrent or it may be synchronized therewith. It is also possible tochange the width of the output pulse from the generator 22. Thecomparator 18 is supplied with power preferably from a point of theswitch 11 remote from the positive supply line 14.

The circuit illustrated in FIG. 3 makes it possible to terminate allheating intervals in exact dependence on the temperature of the heatingelement provided that the resistance of the heating element 10 is aclear function of its temperature. It is worth noting that theresistance of the measuring resistor 12 is in the range of approximately0.004 ohm, which holds resistive losses therein to extremely low values.

A second exemplary embodiment of the rapid heating device of theinvention is illustrated in FIG. 4 in which the thermal behavior of theheating element 10 is simulated electrically by means of RC elements. Anadvantage of the embodiment of FIG. 4 is the absence of the measuringresistor 12 used in the embodiment of FIG. 3. In the embodiment of FIG.4, a switch 11 and a heating element 10 is connected between the powerlines 14 and 15. Their junction is connected via a resistor 30 with aline 31 from which a capacitor 32 and a resistor 33 are connected toground. Also connected to the line 31 is a threshold switch 35 whoseoutput 36 goes to the previously mentioned switching circuit 20.

The closing of the switch 11 initiates the first heating interval inwhich the heating element 10 is heated very rapidly. At the same time,the capacitor 32 is charged at a rate depending on the values of theresistors 30 and 33 and the magnitude of the capacitor 32 itself. Whenthe voltage across the capacitor 32 on line 31 exceeds a certain value,the threshold switch 35 responds and causes the switching circuit 20 toinitiate the pulsed operation characteristic of the second heatinginterval. The resistor 33 connected in parallel with the capacitor 32serves to simulate the cooling of the heating element. Accordingly, thisembodiment of the rapid heating device of the invention requires anexact calibration with the heating element 10 so as to permit exactsimulation of its thermal behavior.

FIG. 5 illustrates a number of variants of a simplified rapid heatingdevice according to the present invention. In FIG. 5a there is shown arapid heating device in which the heating element 10 is connected inseries with a bimetallic switch 40. In the bimetallic switch 40, theheating coil and the switch are connected in series and the switch isnormally closed. Thus when heating current has been flowing for acertain period of time, the switch opens, the current is interrupted sothat the switch cools down and recloses electrically. The power usedwithin the bimetallic switch 40 is lost as heating power for the element10 however. A modified embodiment is shown in FIG. 5b. In this circuit,the heating coil and the switch within the bimetallic switch 41 areconnected in parallel and the switch itself is connected in series witha relay 43 which actuates the switch 11. The bimetallic switch 41 isconnected in parallel with the primary heating element 10.

A similar rapid heating device is shown in FIG. 5c which includes aswitch actuated by an extensible wire switch 45. Here too, the primaryelement 10 is connected in parallel with the series connection of theextensible wire switch 45 and a relay 43 which actuates the switch 11.

A still further modification is shown in FIG. 5d where the primaryheating element 10 is connected in series with a cold conductor 48 and arelay 43. The initially low resistance of the cold conductor 48 causesthe relay 43 to be actuated. In this embodiment, a separate turn-onpulse must be provided to the relay 43.

Finally, FIG. 5e illustrates yet another possibility for embodying arapid heating device. In this variant, a secondary heating coil 50 actson a cold conductor 51. The cold conductor 51 is one resistor in avoltage divider having a further resistor 52 and connected between thesources of power 14 and 15. The voltage across the cold conductor 51 isfed to a Schmitt trigger 55 whose output signal engages the switchingcircuit 20 which, in turn, actuates the switch 11 connected in serieswith the primary heating element 10.

FIG. 6 is a detailed circuit diagram of the embodiment illustrated inFIG. 3. It includes the previously mentioned bridge circuit consistingof the resistors 12, 16 and 17 and the primary heater consisting of fourseparate elements 10. In a particular example, the resistance of anindividual element 10 may be approximately 40 mΩ while the measuringresistor 12 may have a value from 2 to 3 mΩ. The bridge circuit isconnected in series with the switch 11 and provided with power via powersupply lines 14 and 15. A junction point 60 is connected via diodes 62and 63 to one of the inputs of the comparator 18 while the circuit point61 is connected via diodes 64 and 65 to the other input of thecomparator 18. Each of the inputs is connected to ground 15 viarespective resistors 67 and 68. The positive power input 69 of thecomparator 18 is connected to the junction of the switch 11 and themeasuring resistor 12. The output 70 of the comparator 18 is connectedvia a resistor 71 to the base of a transistor 72 whose emitter isconnected to the positive power bus 14 and whose collector is connectedto the negative supply line 15 via the parallel connection of a relay 73and a blocking diode 74. The base of the transistor 72 is connected tothe positive supply rail 14 via a resistor 74 and its collector isconnected to the positive supply line 14 via a capacitor 77 and aresistor 78. A voltage divider consisting of resistors 79 and 80 and adiode 81 is connected between the junction of the capacitor 77 and theresistor 78 on the one hand, and the negative supply line 15 on theother hand. Connected in parallel with the resistor 80 is the Darlingtonoutput stage of the comparator 18 connected in series with the parallelconfiguration of a resistor 82 and a diode 82 and a diode 83 connectedin current-passing polarity.

The manner of operation of the rapid heating device illustrated in FIG.6 is as follows:

When the positive bus 14 receives potential, the output 70 of thecomparator 18 goes to a low voltage via the resistor 78 and the voltagedivider consisting of the resistors 79 and 80. Accordingly, thetransistor 72 is rendered conducting, the relay 73 is energized and theswitch 11 is closed. Thus begins the first heating interval while at thesame time the comparator 18 receives its supply voltage via the input69. The presence of the diode 62-65 insures that the input voltages arebelow the supply voltage so as to insure the reliable operation of thecomparator 18. As the heating elements 10 become warmer, the bridgeapproaches its balanced condition and when the diagonal voltage of thebridge and thus the differential voltage between the input contacts ofthe comparator 18 has become smaller than a given small value, thecomparator output 70 switches to a positive signal. This signal blocksthe transistor 72, causing the voltage across the relay 73 to drop sothat the switch 11 re-opens while at the same time the voltage acrossthe resistor 80 decreases. This causes the Darlington transistor stageof the comparator 18 to close so that the output signal of thecomparator 18 drops and the transistor 72 again conducts, renewing theexcitation of the relay 73 and re-closing the switch 11. While theswitch 11 is open, the heating elements 10 were able to cool off andthus the bridge was unbalanced and when the switch is re-closed themeasuring process begins anew.

A distinction between the circuit illustrated in FIG. 6 with respect tothat shown in FIG. 3 is that in the circuit of FIG. 6, the comparator 18and the generator 22 are not separate and independent elements but thecircuit referred to as the comparator 18 is actually an integratedcircuit, e.g. of the type TAA 865, which serves at the same time forpulse generation. It should be noted however that, depending on theresistance values of the resistors 78, 79 and 80, there is an automaticsynchronization of the switch 11 with the undulations of the startercurrent because the undulations of the supply voltage on the line 14actually cause the triggering of the switching processes in the circuitof FIG. 6.

A detailed circuit diagram of the embodiment of FIG. 4 is given in FIG.7.

The switch 11 and the heater 10 are connected between the positivesupply 14 and the negative supply line 15. Connected across the heateris a voltage divider consisting of resistors 90 and 91. The junction ofthese two resistors is connected via a diode 92 and a resistor 93 to theline 31 which is grounded via a capacitor 32 and is also connected tothe base of a transistor 94 whose collector is attached to the positivesupply line 14 and whose emitter goes to the base of a furthertransistor 95. The transistor 95 is part of a series connection of aresistor 96, a resistor 97 and two diodes 98 and 99 all connectedbetween the positive and negative supply lines. The resistor 96 itselfis a part of a voltage divider consisting of that resistor as well asthe resistors 100 and 101, and the junction of the resistors 100 and 101is joined to the base of a further transistor 102 connected in serieswith a fourth transistor 103. The emitter of the transistor 102 isconnected via a resistor 106 and a resistor 105 to the positive line 14while the base of the transistor 103 is connected via a resistor 108 tothe negative line 15. A diode 109 is connected in blockage polarityacross the resistor 108. The base of the transistor 103 is furtherconnected via a resistor 110 to the positive side 111 of the enginestarter 112. The starter 112 receives power via a line 113, not furthershown.

The junction of resistors 105 and 106 is connected to the base of atransistor 72 whose emitter is connected directly to the positive line14 and whose collector is connected via the parallel configuration of arelay 73 and a flow-blocking diode 74 to the negative line 15.

The circuit described above operates as follows:

When the circuit is energized, the voltage across the capacitor 32 isinitially zero. Accordingly, both transistors 94 and 95 are blocked,causing conduction of the transistors 102 and 103. The current flowingthrough these transistors 102 and 103 lowers the voltage at the base ofthe transistor 72, causing the latter to conduct and to excite the relay73 which now closes the switch 11. Accordingly, the first heating phaseof the device is initiated while the capacitor 32 is charging. When thevoltage on the capacitor 32 is sufficient to switch the transistor 94into conduction, the latter causes the transistor 95 to conduct whichblocks the subsequent transistors 102 and 103. As a consequence, thebase voltage of the transistor 72 rises, causing transistor 72 toultimately block and depriving the relay 73 of excitation current, thuscausing the opening of the switch 11. The capacitor 32 now dischargesthrough the resistor 33 until the transistor 94 again blocks and theentire process begins anew. By connecting the base of the transistor 103to the positive power supply 111 of the starter 112, the undulations ofthe power supply voltage due to the operation of the starter cause asynchronization of the pulsed heater current with the undulations of thestarter current.

The rapid heating devices described above make it possible to insurethat a common heating element 10, which may be of any type whatever, canbe rapidly brought to a predetermined nominal heating power which ismaintained on the average thereafter while being supplied with pulsedcurrent. In order to protect the heating element, it may also beprovided that the temperature is actually reduced during the secondpulsed time interval. Rapid heating devices such as describedhereinabove may be used in motor vehicles, for example as glow heatersin engines with auto-ignition, so as to enhance and speed up thestarting process. They may also be used to heat apparatus located in theexhaust system which requires a certain elevated temperature for properoperation. Such apparatus is, for example, the oxygen sensor and certaincatalyzers. The rapid heating of these devices is required so as topermit controllers to regulate the engine operation to provide anexhaust gas free from noxious components.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other embodiments and variantsthereof are possible within the spirit and scope of the invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A control apparatus in a motor vehicle,comprisingan electrically heated device; a temperature simulating meanshaving a resistor element connected in series with said device and an RCelement connected in parallel with said device for generating acontinuous simulated temperature signal over the course of the entireheating and cooling-down phase of said device and corresponding tovariations in the actual temperature of said device as a result of aflow of electric current through said device; a D.C. power supply meansfor supplying current to said device and said temperature simulatingmeans; a threshold switch for affecting the switching state of saidheating device, connected to receive said simulated temperature signal,for generating a first output signal whenever the simulated outputtemperature signal exceeds a first predetermined value and forgenerating a second output signal whenever the simulated temperaturesignal falls below a second predetermined value; and current flowinterrupting means, which is activated by said threshold switch outputsignal to intermittingly interrupt the flow of current to said deviceand said temperature simulation means from said electric power supplymeans, whereby said device is switched on an off in a closed-loopcontrol in accordance with the temperature of said device.
 2. Anapparatus as defined in claim 1, wherein said means for simulating thetemperature is an electronic means for retaining the simulatedtemperature at least for a given time.
 3. An apparatus as defined byclaim 1, wherein the heating process begins with the actuation of enginestarting and terminates in dependence on operational variables and/or ata predetermined time subsequent to a starter actuation.
 4. An apparatusaccording to claim 1, wherein said temperature simulating means iselectronic and further includes a process circuit comprising resistorsand series-connected transistors, and a resistor-diode network forrendering said circuit independent of operational voltage.
 5. Anapparatus as defined by claim 1, installed in self-igniting internalcombustion engine as a glow heater.
 6. An apparatus as defined by claim1, installed in an internal combustion engine as a heater for theexhaust gas sensor.
 7. An apparatus according to claim 1, whereinfurther, said first predetermined value equals said second predeterminedvalue.